Introduction
Founder effects, genetic drift and recombination associated with
the global spread of HIV-1 infection have given rise to genetically
distinct viral strains referred to as ‘subtypes’ and ‘circulating
recombinant forms’ [1]. HIV-1 genetic diversity may impact on
disease progression and response to antiretroviral therapy, and has
implications for vaccine development [2]. It is therefore important
to monitor changes in the genetic and geographic complexity of
the HIV-1 epidemic, and to identify the processes that drive these
changes. Of the various HIV-1 strains that have been described, the most
prevalent worldwide is subtype C [3]. First described in East and
Southern Africa [4], infections with viruses belonging to (or
partially derived from) subtype C are now prevalent in regions
throughout the world, including India, China, and South Americ In many of the regions where it has been introduced,
subtype C has overtaken other HIV-1 strains introduced at earlier
times [6–9]. Notably, studies suggest that subtype C may acquire
multi-drug resistance more rapidly than other HIV-1 subtypes
The rapid spread of subtype C in regions of South America -
including Brazil, Argentina and Uruguay - has drawn particular
attention [12–16]. Recent studies indicate that the South
American subtype C epidemic likely derives from a single founder
virus that entered the continent via Southern Brazil, and was
derived from viral strains prevalent in East Africa [12,13].
However, the external route via which this virus spread from
East Africa to South America has remained mysterious.